linux-kernel - Re:Re: [PATCH] USB: add usbfs ioctl to get specific superspeedplus rates

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Message-ID: <3a822c60.6ae8.189918ebd0a.Coremail.18500469033@163.com>
Date:   Wed, 26 Jul 2023 17:36:38 +0800 (CST)
From:   "Dingyan Li" <18500469033@....com>
To:     "Oliver Neukum" <oneukum@...e.com>
Cc:     "Greg KH" <gregkh@...uxfoundation.org>, stern@...land.harvard.edu,
        sebastian.reichel@...labora.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH] USB: add usbfs ioctl to get specific superspeedplus
 rates

At 2023-07-26 16:33:22, "Oliver Neukum" <oneukum@...e.com> wrote:
>On 25.07.23 18:11, Dingyan Li wrote:
>  
>> In proc_conninfo_ex(), the number of returned bytes is determined by
>> the smaller number between sizeof(struct usbdevfs_conninfo_ex) and a
>> user specified size. So if we only append new members to the end of
>> struct usbdevfs_conninfo_ex, it won't impact the bytes in the beginning.
>
>You have just caused memory corruption in user space by overwriting what
>was right behind the buffer of the agreed upon size. Or, not much better,
>caused a segmentation fault.
>
>	Regards
>		Oliver

How come?

The actual returned bytes must be smaller than or equal to user specified size.
You can check https://elixir.bootlin.com/linux/v6.5-rc3/source/drivers/usb/core/devio.c#L1493

Regards,
Dingyan